1 June 10, 2007, IDAR’07, Beijing, China Ensuring Consistent Termination of Composite Web Services An Liu 1,2,3 and Qing Li 2,3 1 Department of Computer Science and Technology University of Science & Technology of China (USTC), Hefei, China 2 Joint Research Lab of Excellence CityU-USTC Advanced Research Institute, Suzhou, China 3 Department of Computer Science City University of Hong Kong (CityU), Hong Kong, China
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Ensuring Consistent Termination of Composite Web Services
Ensuring Consistent Termination of Composite Web Services. An Liu 1,2,3 and Qing Li 2,3 1 Department of Computer Science and Technology University of Science & Technology of China (USTC), Hefei, China 2 Joint Research Lab of Excellence - PowerPoint PPT Presentation
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1June 10, 2007, IDAR’07, Beijing, China
Ensuring Consistent Termination of Composite Web Services
An Liu1,2,3 and Qing Li2,3
1 Department of Computer Science and Technology
University of Science & Technology of China (USTC), Hefei, China
2 Joint Research Lab of Excellence
CityU-USTC Advanced Research Institute, Suzhou, China
3 Department of Computer Science
City University of Hong Kong (CityU), Hong Kong, China
Consistent Termination Condition A composite service sc will always terminate
in a consistent state if the consistent termination condition (CTC) holds:
vi.tp{c, rc}, sc.t.te vi.oc.ta for vi Vs in G Example:
sc, s1s2
if s1.on.tx=2 & s1.oc.MCT=5 & s2.on.tx=4
then s1.oc.ta=[2,7], sc.t.te=6
12June 10, 2007, IDAR’07, Beijing, China
CTC Verification
Precondition: global view of a composite service: control flow, transactional and temporal property
Method: simple calculation Problem: NOT easy to get a global view
Dynamic selection Multi-level composition
13June 10, 2007, IDAR’07, Beijing, China
Methodology
Assumptions A1: only elementary component services A2: static service selection A3: only compensatable component services A4: only AND-split and AND-join operators
14June 10, 2007, IDAR’07, Beijing, China
Outline
Problem Statement and Background Problem Modeling and Methodology Framework Conclusion and Future Work
15June 10, 2007, IDAR’07, Beijing, China
Framework Overview
selection
CEP
YESNO
re-selection
YES
NO
redesign
available service?
G
CTC verification
design
Engine
TEA
Consistency Monitor
Process pool
Selector
G
G
G
16June 10, 2007, IDAR’07, Beijing, China
CTC Verification ExamplesTable1 A B C D
tx 2 8 4 6
MCT 15 20 8 12A
B
C
D
T2 A B C D
ts 0 2 2 10
te 2 10 6 16
ta [2,17] [10,30] [6,14] [16,28]
T3 A B C D
ts 0 2 4
te 2 8
ta [2,17]
T4 A B C D
ts 0 2 6
te 2 10
ta [10,30]
T5 A B C D
ts 0 2 5
te 2
ta [2,17]
[10,30]
10
[11,31]
11
10 10
[16,28]
10
16
10
[8,16] [11,31]
17
11
[8,16]
[10,18]
12
[12,20]
12
16
[16,28]
18
[18,30][2,17][2,17]
16
[16,28]
9
[9,17][10,30]
1011
[11,31] [11,19]
11
11
17
[17,29]
17June 10, 2007, IDAR’07, Beijing, China
Scheduling Algorithms
Motivation: different scheduling algorithms lead to different results of CTC verification, which decide whether to abort the service or not
Objective: design a scheduling algorithm which can decrease the possibility of service abortion
Some algorithms Immediate scheduling Minimal delay scheduling Maximal delay scheduling Average delay scheduling …, optimal scheduling algorithm?
18June 10, 2007, IDAR’07, Beijing, China
Dynamic Monitoring
TEA CEP execution engine
1. instance of process graph
2. verify CTC3. YESstart time
4. service completes
4. service completes
5. verify CTC6. YES
new start time
7. add record
8. exception
CM
6. NOabort
9. compensation
9. compensation
selection
CEP
YESNO
re-selection
YES
NO
redesign
available service?
G
CTC verification
design
Engine
TEA
Consistency Monitor
Process pool
Selector
G
G
G
19June 10, 2007, IDAR’07, Beijing, China
Inaccurate Global View
Problems Uncertainty of Execution Time (UET) Information Missing (IM)
IM1: execution time of normal operation is unknown IM2: available time of compensation operation is